A man was walking through a tunnel. He is 1/4 of the way through when he hears a train approaching the tunnel from behind him.

If he turns and runs back, he will make it out of the tunnel just as the train is entering it (and will save himself by a hair). If he goes forward to the far end of the tunnel, he will also just barely make it, emerging from the tunnel just as the train is about to catch up to him.

If the man's running speed is 7 miles per hour, how fast is the train moving?

(from techInterview.org)

(In reply to Kind of answer by Dulanjana)

That can be seen as true :)

But then with most problems on the site you can find some little detail to pick at to show that the solution isn't neccessarily what is meant. However I think in most cases, and here in particular, if a grain of common sense is used in thinking about the problem, certain obvious assumptions come forth.

Surely you wouldn't wish every problem to be paragraphs upon paragraphs of text that does nothing but explicitly states every commonsense assumption implied by the problem.

In this case, I think that the problem clearly assumes a constant speed for the train and for the man running.

Posted by levik on 2002-05-31 23:09:35